Hi guys,
We are facing some issues with a btrfs filesystem on one of our department
filers.
The problem started pretty much one week ago, when I decided to purge old
snapshots.
Until then we were doing daily btrfs snapshots to have a quick backup.
What then happened was that btrfs-cleaner kicked in, and is now slowing things
down very badly.
It is consuming 100% CPU and also a lot of IOP/s.
I tried reducing its CPU priority, but that was pretty much without effect.
Beside that we tried restarting the machine, but that also did not mitigate the
problem.
I understand that purging snapshots is a complex operation, but we somehow need
to reduce the load this causes during working hours.
Are there any ways to tell btrfs-cleaner to suspend or reduce its operations?
Background:
The file-server runs inside a XEN domU
The backing disk is a Ceph RDB with 50TiB capacity
We employ a bcache with a local SSD to improve latency
Files are served via NFS and Samba to a couple of hundred clients.
Thanks & regards
Simon
uname -a
Linux v2-fs 4.1.42-xen #2 SMP Wed Jul 12 14:06:37 CEST 2017 x86_64
GNU/Linux
btrfs --version
Btrfs v3.17
btrfs fi show
Label: 'v2-fs-data' uuid: f2bad13d-8b02-4325-8c4a-31b0cafb1549
Total devices 1 FS bytes used 6.98TiB
devid 1 size 50.00TiB used 7.48TiB path /dev/bcache0
Btrfs v3.17
btrfs fi df /mnt/ceph/
Data, single: total=7.10TiB, used=6.93TiB
System, DUP: total=8.00MiB, used=864.00KiB
System, single: total=4.00MiB, used=0.00B
Metadata, DUP: total=194.00GiB, used=54.93GiB
Metadata, single: total=8.00MiB, used=0.00B
GlobalReserve, single: total=512.00MiB, used=0.00B
dmesg did not contain any recent (2 days) events.
The older ones were about NFSd being stuck for more than 30 seconds while
reading from disk.
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